This invention relates to an ultrasonic scanning device, which, when inserted into a tubular coeliac cavity, examines the viscera disposed around the tubular coeliac cavity by ultrasonic scanning.
An ultrasonic scanning device for examining viscera which is provided with a flexible insertion section is generally classified into the type which carries out scanning electronically and the type which performs scanning mechanically.
The distal end portion of the insertion section of the electronic scanner contains an ultrasonic transmission-reception unit. Therefore, the insertion section is rendered too thick to be smoothly introduced into the tubular coeliac cavity.
The distal end portion of the insertion section of the ordinary mechanical scanner contains a vibrator. This vibrator rotates about the central line of the distal end portion by a proper means.
One of the known ultrasonic scanning devices contains an electric motor and an angle detector in its distal end portion, resulting in a bulky construction.
The use of a pulse motor whose driving pulse signals are changed to motor angle information eliminates the angle detector. But, the distal end portion of the mechanical scanner which contains the pulse motor is unavoidably rendered too thick for easy insertion into a tubular coeliac cavity. Moreover, such a small pulse motor as is contained within the distal end portion is driven at as broad an angle as 60.degree. per pulse. Therefore, an image of a viscus to be examined which appears on a display device is extremely rough, probably failing to assure the correct examination of the viscus. If a gear mechanism is applied to cause the vibrator to be rotated at a smaller angle per drive pulse of the pulse motor, it is indeed possible to obtain a distinct image of a viscus. However, the vibrator is rotated at a slower speed, not only consuming much time in the examination of the viscus, but also resulting in the failure to accurately examine a viscus whose physiological condition varies with time.
The distal end portion of the insertion section of another mechanical scanner comprises a vibrator which is unrotatable relative to the distal end portion, and a reflector for reflecting in prescribed directions ultrasonic waves delivered from the vibrator as those supplied thereto. With this type of mechanical scanner, the reflector is rotated by the control section with the aid of a linear member extending through the insertion section. With this mechanical scanner, the stationary vibrator is disposed in the distal end portion nearer to the control section than the reflector. Therefore, the reflector-rotating linear member cannot be fixed to the center of the reflector, but the linear member is fitted to the peripheral edge of the reflector, making it necessary to let the reflector rotate about the vibrator. Now let it be assumed that the insertion section of the scanner is flexible. Under this condition, the linear member should also be flexible. When the linear member is let to revolve around the axis in an extended state by the control section to effect the rotation of the reflector, then said linear member tends to be undesirably deformed into a helical shape. As a result, the movement of the reflector does not exactly follow the rotation angle of the linear member at the control section, probably leading to failure to obtain a correct image of a viscus and, consequently, failure to carry out its reliable examination. With the second known type of scanner, it is substantially impossible to apply a flexible insertion section.
With any of the conventional ultrasonic scanners, the reflector is surrounded with air in the distal end portion, resulting in a decline in the propagation rate of ultrasonic waves through the distal end portion and the corresponding decrease in the precision of examination.
It is accordingly the object of this invention to provide an ultrasonic scanner for examination of viscera, wherein the reflector is always rotated at a prescribed speed in spite of the narrow construction of a distal end portion; ultrasonic waves propagate smoothly between an ultrasonic wave transmission-reception unit and the inner wall of a coeliac cavity, thereby assuring the display of a reliable viscus image and consequently the high precision examination of the viscus.